Safety paper



Patented Mar. 14, 1933 STA Parr

SAFETY PAPER No Drawing. Application filed April 22,

This invention relates to so called safety papers and to the process of preparing such papers so that when once written on with ink the writing cannot be removed, altered or replaced without setting the ink and leaving tell-tale stains, discolorations or alterations in the surface of the paper.

Such papers and treatments have heretofore been proposed but no ierrocyanide treated paper been produced which would not discolor with age or on exposure to light. Such discoloration previous to use of course rendered the paper unacceptable for most purposes and in fact such inherent discoloration defeated the possibilities of detection of tampering by discolorations developed by ink eradicators. Ferrocyanide of potassium was proposed as an inkset by Dr. Ernest E. Schmidt in his Patent git-1,217,076 of April 20, 1917 and as an inkset had a considerable effectiveness. Paper, however, so treated developed discoloration to such an extent that it proved inacceptable in use.

I have discovered that by giving the paper a moderate alkalinity I can use ferrocyanide of potassium without discoloration of the paper while yet providing an ink set in the paper and making it possible to detect stains, spots, and other tell-tale signs where an ink eradicator has been used.

In many commercial papers which are normally on the acid side in order to develop an inkset which will not discolor when treated with such ink setting materials as fcrrocyanide either of potassium or sodium, this acid condition of the paper must be neutralized and paper made moderately alkaline. The treatment varies according to different papers and their normal acid or alkaline condition.

The alkaline condition in the paper does not in any way interfere with the inkset qualities of the ferrocyanide solution but creates a condition in the paper whereby obvious evidence of tampering with the original writing by ink eradicators results. I have discovered that a paper of proper alkaline condition treated with an inkset will on the application of any known ink eradicator either develop a stain on the surface of the paper, or the spots 1931. Serial no. 532,115.

"where the eradicator has been applied'will be bleached to a degree which is readily apparent. I WVhile necessary in order to procure satisfactory inksets in the several kinds of commercial paper, while simultaneously rendering the same subject to stain by the use of any chem ical intended to produce an eradication, it is important that a state of alkalinity SuflL a great variety of formulae are may also be necessary to vary the formulae to take into account the chemical nature of the coloring material. l

For the purposes of my present invention it is not believed to be necessary to set forth these many formulae, as my invention may be practiced by producing a state of alkalinity which will prevent discoloration,

while at the same time promptly showing an inkset and stain upon the use of an ink eradicator.

In checking the use of any particular compound of any given paper, I dip a slip of paper into the compound for an instant,

preferably not over two seconds of time, let it dry and then write upon it. with ink and let that dry, then try to remove the writing with ink eradicator. The acid oi the ink eradicator sets the ink while the chlorine emphasizes it and causes a surface stain on the paper. Frequently, chlorine will remove the inkset by destroying the surface of the paper and soaking it through. When the paper drys a yellow stain on the white paper outlines where the surface has been wet and the paper will be disfigured with innumerable fine wrinkles. Although in some, cases those stains may be removed by a solution of sodium bisu-lphate and the paper restored to its white appearance, when,

however, the paper drys it will be noticed that wherever sodium bisulphate is applied the surface of the paper is whiter. If the paper is held up to the light a dark stain would be seen inside the paper, notwithstanding the fact that both surfaces appear whiter. This dark stain cannot be removed without destroying the paper. 7

Various modifications in the amount of 10 alkaline may be employed as well as in the other chemicals used without departing from the spirit of my invention if within the limits of the appended claims.

What I therefore claim and desire to secure by Letters Patent is:

p 1. The method of producing a safety paper consisting in creating an alkaline state in such paper and in so treating said paper with a ferrocyanide as to produce an ink 29 set condition without affecting the normal color of the paper.

2. The method of producing a safety paper consisting in creating an alkaline state in such paper by an acid neutralizing carbonate and in so treating said paper with was - a ferrocyanide as to produce an ink set condition without affecting the normal color of the paper.

3. Themethod of producing a safety pa- 3? per consisting in creating an alkaline state in such paper by carbonate potassium or sodium and in so treating said paper with a ferrocyanide as to produce an ink set condition without affecting the normal color of the paper.

4. A safety paper treated with an alkali and a. ferrocyanide in such proportions as to produce an ink set condition therein without affecting the normal color of the pa er.

( 5,. A safety paper treated with an al ali and a ferrocyamde in such proportions as to produce an ink set condition therein without afiecting the normal color of the paper, said paper being of a nature to show discoloration when an ink eradicator is applied thereto.

'6. A safety paper treated with such proportions of carbonate of potassium and ferrocyanide as to produce an ink set condition 9 therein without affecting the normal color of the paper.

7. The method of producing a safety paper consisting in maintaining such paper sufficiently alkaline to neutralize ferrocya- 5 nide which is added thereto in quantity sufficient to produce an ink set condition therein but without destroying the normal color of the paper. 7

8. A safety paper treated with such proportions of carbonate of potassium and a v ferrocyanide of potassium as to produce an ink set therein without affecting the normal color of the paper.

In testimony whereof I afix my signature.

5? FRANK s. WOOD. 

